The present invention relates generally to implementation of signalling in a communications system. More specifically, the invention relates to changing the characteristics, particularly the capacity, of a signalling link in a communications network, specifically in an ATM-based communications network. In this context, a signalling link denotes the signalling channel between two adjacent network elements.
As is well known, ATM (Asynchronous Transfer Mode) is a connection-oriented packet-switching technique, which has been selected by the international organization for telecommunications standardization, ITU-T, as the technology for implementing a broadband multimedia network (B-ISDN). In an ATM network, the problems of conventional packet-switched networks (such as X.25 networks) have been overcome by transmitting short packets of a constant length (53 octets) called cells. Each cell comprises a 48-octet payload portion and a 5-octet header. In addition to other data, the header comprises address information on the basis of which a cell is routed in the network. Further discussion of an ATM network herein will be omitted as non-essential subject to the understanding of the invention. A closer description can be found in international standards and textbooks of the art.
B-ISDN, which on the conceptual level can be construed as the aim of integrating broadband and narrowband services in the same network, is based on the earlier (narrowband) ISDN model in which the interface between the network and the subscriber is fully digital. However, the services offered in a B-ISDN network require transmission rates that are above the transmission rate of the ISDN network primary rate access. Also in signalling, B-ISDN complies with the out-of-band signalling that is used in the ISDN model (cf. signalling channel D). Out-of-band signalling means that signalling and user data do not share the same channel, but a separate channel is provided for signalling. In a B-ISDN network, virtual channels offer the possibility of separating user channels and signalling channels from each other. In B-ISDN, the signalling messages are thus transmitted as out-of-band messages on separate virtual connections of the ATM layer. Also, the signalling is common channel signalling in which control data pertaining to several communications connections is transmitted on one signalling connection. Dedicated virtual channels are employed for different signalling purposes.
Since the SS7 (Signalling System No. 7) is the international standard for out-of-band signalling systems, it has been modified to suit broadband networks as well, so that it is suited, besides establishing, managing and releasing virtual connections, also for other operations required by an ATM-based network.
The drawback of the present signalling systems and methods is, however, that they are not capable of flexibly and rapidly adapting themselves to a temporary increase in the signalling load. This is due to the fact that there is no resilient modification procedure available for fixed connections, signalling connections included, wherewith their capacity could be changed. Thus, so far it has been necessary to modify fixedly defined connections by means of network management. However, specifically connectionless signalling traffic, which includes e.g. retrieval of various data from databases located in the network, is of such a nature that it may involvexe2x80x94especially in the future-load peaks that are difficult to anticipate. For this reason, it is desirable that also the signalling capacity could be modified more flexibly than heretofore.
It is an objective of the present invention to offer a remedy to the drawbacks described above by providing a solution wherewith the signalling capacity can be flexibly changed in the network when the signalling load increases temporarily.
This objective is achieved with the solution in accordance with the invention, which is defined in the independent claims.
The idea of the invention is to reserve for signalling links between adjacent network elements one or more identifiers that cannot be used for signalled connections, and thereafter to use the standard modification procedure intended for user connections for a novel purpose, i.e. for changing the characteristics (capacity) of the signalling link. The known modification pro cedure intended for user connections is thus utilized to change the capacity of the signalling link between two adjacent network elements. Modification is initiated only in those network elements in which a need for modification is detected, and thus the modification usually only relates to a specific link between two adjacent exchanges and extends from one end to the other of a signalling connection only if a need for additional capacity is simultaneously detected at all successive signalling points in the connection. Also in this case, the modification of each signalling link is independent of the other signalling link. Thus, the modification of successive links in the same connection are not dependent on one another, as is the case in user connections.
The capacity can be restored to its original value for example after no blocking or excess load has been detected during a predetermined period of time (e.g. during one hour). The restoration can be based on measuring the signalling load in the node, but also on the traffic situation or capacity requirement of the user connections.
With the solution in accordance with the invention, a dynamic signalling network is achieved that can automatically increase the signalling capacity in those parts of the network in which the signalling load increases temporarily.
An important further advantage of the solution in accordance with the invention is that it makes efficient use of the modification procedures according to the current recommendations, with the result that it can also be added with very small changes to a network in which said procedures have been implemented.